1. Field of the Invention
The invention relates to a stator for an eccentric spiral pump or eccentric screw pump with a helical rotor. The stator also has a helical cavity to receive the rotor and consists mainly of an elastic material which is surrounded by a rigid casing.
2. Description of the Prior Art
In rotors corresponding to the prior art either a solid or a rigid casing composed of a plurality of segments is used to accommodate the elastic material of the rotor.
Thus, U.S. Pat. No. 4,313,717 discloses a rotor housing consisting of three identically axially arranged housing segments which are clamped together by means of a band. In this housing three housing segments matched to the circumference of the rotor, as well as the corresponding clamping means to clamp the rotor housing around the rotor itself are thus necessary. Without these clamping means the housing segments cannot be held on the rotor.
Known from DE 33 12 197 C2 is an eccentric spiral pump with a casing which has segments interconnected by positive contact. In this case, the edges of neighboring segments are arranged such that they intermesh in a tongue and groove fashion. These tongue-and-groove fixings have contact surfaces so that they are not movable towards one another. Furthermore, these fixings are provided exclusively at the ends of the segments whereas along the remaining outer surfaces there is even a distance between the segments in order to make it possible to adjust the diameter for matching according to the rotor wear. For this purpose additional clamping means are required however.
These rotors of eccentric spiral pumps according to the prior art have the disadvantage that for each size, i.e. for each diameter of a rotor, a special casing matched to this diameter must be provided. Thus, for each type of pump, construction costs, tool costs and manufacturing costs are incurred anew. In addition, with a broad production program there is a high expenditure in warehousing for different types of pumps.